Document port6 and bind6 config options.

Add commented port6 and bind6 options to default redis.conf file.

redis.conf

@@ -23,6 +23,7 @@ pidfile /var/run/redis.pid
 # Accept connections on the specified port, default is 6379.
 # If port 0 is specified Redis will not listen on a TCP socket.
 port 6379
+# port6 6379
 
 # By default Redis listens for connections from all the network interfaces
 # available on the server. It is possible to listen to just one or multiple
@@ -33,6 +34,7 @@ port 6379
 #
 # bind 192.168.1.100 10.0.0.1
 # bind 127.0.0.1
+# bind6 ::1
 
 # Specify the path for the unix socket that will be used to listen for
 # incoming connections. There is no default, so Redis will not listen